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Nitrogen Diet Reduces Arizona County's Drinking Water Threat

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Photo Courtesy of MHW Constructors
The new Roger Road Water Reclamation Facility project includes several design improvements over the nearby facility it is replacing.
By Pam Hunter
Wastewater treatment spends $720-million to improve quality of effluent.
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A decade ago, Pima County's Regional Wastewater Reclamation Dept., or RWRD, was facing a problem: The Arizona Dept. of Environmental Quality had ruled that the levels of nitrogen coming from RWRD's network of 10 wastewater-stripping and treatment plants were too high. At that point, the 41- million-gallons-a-day Roger Road plant was releasing wastewater with nitrogen levels between 30 milligrams and 57 mg per liter, well above the 10 mg/l requirement, say county officials.

While nitrogen is known to be harmful to aquatic life, experts say that, when its levels are higher than would occur naturally, it also can be harmful to children and babies. Two of the system's plants—the facilities at Roger Road and Ina Road—discharge directly into the Santa Cruz River and thus presented a potential threat to health.

Although the county regularly monitors the quality of water and no local water providers draw from the groundwater near the Roger Road and Ina Road facilities, the county and Arizona Dept. of Environmental Quality (DEQ) officials were concerned that effluent discharged into the river could percolate into local groundwater and increase nitrogen and ammonia levels in the aquifer.

The Arizona DEQ, in accordance with federal requirements, had set permissible nitrogen and ammonia limits to a range of 8 mg/l to 10 mg/l. By 2006, the DEQ told Pima County officials they would need to meet the new requirements at the Ina Road facility by Jan. 1, 2014, and at the Roger Road facility by Jan. 1, 2015.

As a result, RWRD embarked on a $720-million Regional Optimization Plan (ROMP) to improve the quality of its effluent. The program is using innovative techniques as it expands and upgrades the 37.5-million-gallons-a-day Ina Road plant to 50 mgd and replaces an aging, outdated 41-mgd wastewater stripping plant with a new, state-of-the-art 32-mgd water reclamation plant at Roger Road. The plan also includes an interceptor sewer that reroutes flows from the Roger Road plant to the Ina Road facility, which was completed in December 2010.

New Way of Doing Business

For ROMP, the county opted to use alternative delivery methods on the projects, says Jackson Jenkins, utility director for the Pima County RWRD. With $720 million at stake in the ROMP program—the largest such undertaking in the county's history—officials decided "the time was ripe to take a look at some other methods," Jenkins says.

For the Pima County Water Reclamation Facility (WRF) at Roger Road, "we decided that a DBO [a design-build-operate contract] was the best value to the ratepayer and to the region. Based on how things have come out in the building and completion of this project, I think we made the right choice," Jenkins adds.

CH2M Hill won a $164-million portion of the design-build-operate contract in December 2010. The project's total cost for the capital phase is $172 million. The Englewood, Colo.-based firm will operate the facility for 20 years, using primarily local labor.

MWH Constructors Inc., Broomfield, Colo., is the construction manager-at-risk on the project's $227-million Ina Road upgrade and expansion, CH2M Hill is the designer, and Jacobs Field Services of North America is the program manager.

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